Mobile communication terminals need to be located in mobile communication networks to start communication. For this purpose, when a mobile communication terminal is powered on or moves to a different area from the area where it was located until then, an attach request signal (Attach Request) is transmitted to a mobile management node through a base station. Then, by the mobile management node transmitting the attach request signal from the mobile communication terminal to a subscriber information server on a higher level of the mobile management node, the location information of the mobile communication terminal is registered and managed in the subscriber information server.
These years, however, the coverage areas (cells) of plural mobile communication networks (PLMN: Public Land Mobile Network) are formed to overlap each other. Therefore, the mobile communication terminals accessible to such plural mobile communication networks are widely used. For example, as existing mobile communication networks, there are 2G (2nd Generation: the second-generation mobile communication system) networks such as GERAN (GSM EDGE Radio Access Network (GSM is a registered trademark of GSM Association), and 3G (3rd Generation: the third-generation mobile communication system) networks such as UTRAN (Universal Terrestrial Radio Access Network). In the 2G/3G networks, both services of voice call and data communication are available.
In addition, to realize higher-speed data communication than the 2G/3G networks, there are 4G (4th-generation) networks such as EUTRAN (Evolved Universal Terrestrial Radio Access Network). In such 4G networks, as high-speed data communication services are available, the mobile communication terminal supporting the 4G network are connected to a 4G network in priority. When a mobile communication terminal located in a 4G network starts a voice call now by using a voice call service, the mobile communication network where the mobile communication terminal is located is switched to a 2G/3G network from the 4G network, and then the voice call communication is carried out via the 2G/3G network. Accordingly, the voice call service utilizing the 2G/3G network is made available to the mobile communication terminal.
In such a situation, when a mobile communication terminal transmits the attach request signal for making a request of location registration to a mobile management node of the mobile communication network where the mobile communication terminal communicates, the location registration is not enabled by a factor caused by the network side, in some cases. As a factor caused by the network side, for example, there is a network failure that a session between the mobile management node and a network device on a higher-level than the mobile management node cannot be established by a failure in a transmission path between the mobile management node and such a higher-level network device.
When the location registration of the mobile communication terminal cannot be made, the mobile communication terminal cannot make a voice call. In this case, the mobile management node makes a response of an attach rejection signal (Attach Reject), in which “Cause value” that is a value indicative of a cause of rejecting the location registration process is set, to the mobile communication terminal. Then, the mobile communication terminal transmits an attach request signal to another mobile communication network, or continuously transmits the attach request signal to the same mobile communication network, so as to complete the location registration. When the mobile communication terminal is capable of making the location registration via another mobile communication network, such as the 3G network of an identical carrier (communication carrier) or a mobile communication network of another communication carrier, the mobile communication terminal is allowed to make the voice call and perform the data communication. It is to be noted that the operation of the mobile communication terminal when the attach rejection signal is received is regulated in accordance with the terminal settings or the “Cause value” described in non-patent literature 1 below. Herein, the “Cause value” is a value indicative of a cause of rejecting a registration process of the location information.
As the terminal settings, “voice priority (Voice Centric)” and “data priority (Data Centric)” are regulated in the following non-patent literature 2.
The regulation of the “voice priority” is defined as a policy of giving priority to the completion of the location registration, so that an incoming voice call is made available as soon as possible. The regulation of the “voice priority” is set in a mobile phone, for example.
The regulation of the “data priority” is defined as a policy of staying in a mobile communication network superior in the data communication (that is, having a high throughput) even if the voice communication is unavailable. For example, when a 3G network and an LTE network are formed to overlap each other, trying to stay in the LTE network is defined. The regulation of the “data priority” is set in a tablet terminal, for example.
As specific operations of the mobile communication terminal in accordance with the Cause value at the time of receiving the attach rejection signal, there are following operations, for example.
As a first example of the operation of the mobile communication terminal that has received the attach rejection signal from an LTE network mobile management node, there is an operation of stopping the location registration request (transmission of attach request signal) from a mobile communication terminal for a certain period of time.
As illustrated in FIG. 7, a mobile communication terminal transmits an attach request signal to an LTE network mobile management node (MME) (S101). The LTE network mobile management node (MME) transmits the attach request signal to a subscriber information server (HSS) (S102). However, it is supposed that a failure occurs in a network of the LTE network and the location information of the mobile communication terminal cannot be registered in the subscriber information server (HSS). In this case, the attach rejection signal, in which the “Cause value” indicating that a communication unavailable state continues for a while is set, is transmitted to the mobile communication terminal (S103). As the Cause value transmitted in such a case, #42 (Severe network failure) is defined in non-patent literature 1.
In this situation, the mobile communication terminal stops the location registration request, for example, for several minutes to ten and several minutes based on the received Cause value “#42”, regardless of the terminal settings of its own. Then, the mobile communication terminal selects an operation of making the location registration request again to the LTE network mobile management node, after a certain period of time has elapsed (S104). At this timing, if a network of the LTE network recovers, the mobile communication terminal can perform the location registration in the LTE network.
As a second example of the operation of the mobile communication terminal that has received the attach rejection signal from the LTE network mobile management node, there is an operation of performing the location registration by transmitting the attach request signal to the mobile management node of another mobile communication network (for example, 3G network). This operation is carried out by the mobile communication terminal that desires to give priority to the voice incoming call. In other words, this operation is carried out in the case of the “voice priority” of the terminal setting.
Although the mobile communication terminal transmits the attach request signal to the LTE network as illustrated in FIG. 8, there is no response from the subscriber information server (HSS) to the mobile management node because of a network failure or the like, the attach rejection signal, in which the “Cause value” indicative of no response is set, is transmitted to the mobile communication terminal (S111 to S113). As the Cause value transmitted in such a case, “#19” (ESM failure) is defined in non-patent literature 1.
Then, the mobile communication terminal switches the mobile communication network to the 3G network based on the received Cause value “#19” and the “voice priority” of the terminal setting, and in addition, selects an operation of invalidating the LTE network for a certain period of time (for example, dozens of minutes to several hours) (S114 to S115). Then, the mobile communication terminal performs the location registration in the 3G network (S116). This operation is carried out by the mobile communication terminal that desires to give priority to the voice incoming call. In other words, this operation is carried out in the case where the terminal setting is the “voice priority” and the Cause value that has been set to the attach rejection signal is “#19”. Accordingly, the mobile communication terminal performs the location registration in the 3G network, and performs the voice communication promptly.
It is to be noted that when the “data priority” is the terminal setting of the mobile communication terminal, the mobile communication terminal tries to stay in the LTE network. For this reason, even if the mobile communication terminal receives the attach rejection signal in which the same Cause value “#19” has been set, the mobile communication terminal does not perform the location registration operation in the 3G network.
As a third example of the operation of the mobile communication terminal that has received the attach rejection signal from the LTE network mobile management node, there is an operation of continuously transmitting the attach request signal to the LTE network mobile management node which has transmitted the attach rejection signal. This operation is carried out by the mobile communication terminal that desires to give priority to the data communication. In other words, this operation is carried out in the case where the terminal setting is the “data priority”.
Although the mobile communication terminal transmits the attach request signal to the LTE network, as illustrated in FIG. 9, there is no response from the subscriber information server (HSS) because of a network failure or the like, and the attach rejection signal, in which the Cause value “#19” indicative of no response is set, is transmitted to the mobile communication terminal (S121 to S123).
Then, the mobile communication terminal tries the location registration in the LTE network by transmitting the attach request signal to the LTE network mobile management node (MME) again, judging from the Cause value “#19” that has been received and the terminal setting of the “data priority” (S124). This operation is carried out by the mobile communication terminal that desires to give priority to the data communication. In other words, this operation is carried out in the case where the terminal setting is the “data priority” and the Cause value set in the attach rejection signal is “#19”. When the terminal setting of the mobile communication terminal is the “data priority”, the mobile communication terminal tries to be located in the LTE network having a higher throughput. For this reason, unlike the operation of the second example, the mobile communication terminal continuously transmits the attach request signal to the LTE network mobile management node. Hence, the mobile communication terminal is capable of making a location registration in the LTE network immediately after the location registration unavailable state is recovered in the LTE network.
As a fourth example of the operation of the mobile communication terminal that has received the attach rejection signal from the LTE network mobile management node, there is an operation of transmitting the attach request signal to another network mobile management node of another mobile communication network (for example, 3G network) that covers the location of the mobile communication terminal, so as to perform the location registration. This operation is carried out for the mobile communication terminal that starts communication by loaming in (a loaming-in user), in a case where there is no roaming agreement of a LTE network between a communication carrier of the user of the mobile communication terminal and a communication carrier that provides the LTE network.
In such a case, an attach rejection signal, in which the “Cause value” indicating that an appropriate coverage area (a tracking area TA) cannot be found is set, is transmitted to the mobile communication terminal. As the Cause value to be transmitted in such a case, “#15” (No suitable cells in tracking area) is defined in non-patent literature 1.
Then, the mobile communication terminal tries not to use the tracking area of the LTE network for a certain period of time (for example, ten and several hours) based on the Cause value “#15” that the mobile communication terminal has received, regardless of the terminal settings. It is to be noted that at this timing, the LTE function of the mobile communication terminal is not turned off. Then, the mobile communication terminal performs the location registration in the 3G network having the loaming agreement, and can start communication in the 3G network.
In addition, when the location registration of the mobile communication terminal in the LTE network is successful, but the location registration in the 3G network fails, a location registration completion signal in which the “Cause value” is set (Attach_Accept) is replied from the network. As the Cause value transmitted in such a case, “#18” (CS Domain Not available) is defined in non-patent literature 1.
As regulated in non-patent literature 2, when the “data priority” is set at the mobile communication terminal, the mobile communication terminal performs an operation of staying in the LTE network. On the other hand, when the “voice priority” is set at the mobile communication terminal, the mobile communication terminal performs an operation of selecting a wireless system such as a 3G network or another PLMN, by which the voice communication is made available. As described above, even when the location registration completion signal in which the “Cause value” is set is replied, the mobile communication terminal performs an operation that is regulated based on the “Cause value”.
In addition, when it is allowed to give the location registration request to the PLMN of another communication carrier, an attach request signal can be transmitted to the PLMN of another communication carrier, instead of the 3G network.